1. Field of the Invention
The present invention relates to an illumination optical system for a liquid crystal display and, in particular, to an illumination optical system for a liquid crystal display having a light source section equipped with a reflector for illuminating a liquid crystal display panel.
2. Description of the Prior Art
Recently known is a projection type liquid crystal video projector in which a liquid crystal display panel is irradiated with backlight, and the light transmitted through the liquid crystal display panel carrying the image information displayed on the liquid crystal display panel is projected onto a screen. A light source unit for the backlight is constituted by a light source and a reflector for forwardly reflecting the light emitted from the light source. For example, this reflector has a form of paraboloid of revolution and is disposed such that the light source is placed at the focal position of this paraboloid of revolution.
As the backlight for irradiating the liquid crystal display panel, white light is usually employed. While the white light has various kinds of polarized light components, the liquid crystal display panel uses a characteristic of a liquid crystal and thus can utilize only a polarized light component having a plane of vibration in a predetermined direction with respect to the liquid crystal display panel, thus failing to efficiently utilize the light quantity of backlight.
In the technique disclosed in Japanese Unexamined Patent Publication No. 5-210098, a polarizing beam splitter for transmitting therethrough a P-polarized light component of the light from the light source and reflecting an S-polarized light component thereof toward the light source is disposed between the light source section and the liquid crystal display panel, and a quarter-wave optical phase plate is disposed between the polarizing beam splitter and the light source, such that the S-polarized light component reflected toward the light source by the polarizing beam splitter is converted into a P-polarized light component, which is made incident on the liquid crystal display panel, whereby the light from the light source section can be efficiently utilized.